Research article Boron-doped diamond oxidation of amoxicillin pharmaceutical formulation: Statistical evaluation of operating parameters, reaction pathways and antibacterial activity Zacharias Frontistis a , Maria Antonopoulou b , Danae Venieri c , Ioannis Konstantinou d , Dionissios Mantzavinos a, * a Department of Chemical Engineering, University of Patras, Caratheodory 1, University Campus, GR-26504 Patras, Greece b Department of Environmental & Natural Resources Management, University of Patras, 2 Seferi St., GR-30100 Agrinio, Greece c School of Environmental Engineering, Technical University of Crete, Polytechneioupolis, GR-73100 Chania, Greece d Department of Chemistry, University of Ioannina, GR-45110 Ioannina, Greece article info Article history: Received 26 February 2016 Received in revised form 12 April 2016 Accepted 12 April 2016 Available online 23 April 2016 Keywords: Antibiotics BDD By-products Factorial design Mechanism Mineralization abstract The electrochemical oxidation of a commercial amoxicillin formulation over a boron-doped diamond (BDD) anode was investigated. The effect of initial COD concentration (1e2 g/L), current density (30 e50 mA/cm 2 ), treatment time (15e90 min), initial pH (3e9) and electrolyte concentration (2e4 g/L NaCl) on COD removal was assessed through a factorial design methodology. For the range of conditions in question, the first three single effects, as well as the interaction between COD and time were the most important ones in terms of mass of COD removed. Liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) was employed to identify major transformation by-products (TBPs); thirteen compounds were detected as TBPs of AMX electrochemical degradation, while several others appear in the original formulation. AMX degradation occurs though the following pathways: (i) hydroxylation mainly in the benzoic ring, (ii) opening of b-lactam ring followed by decarboxylation, hydroxylation and re-arrangement, and (iii) bond cleavage between the carbons of amino and amide groups. Furthermore, the process is accompanied by the release of several ions, i.e. nitrate, sulfate and ammonium. The antibiotic activity of AMX up to 1000 mg/L was tested against Klebsiella pneumoniae and Entero- coccus faecalis reference strains; both bacteria are completely inactivated at this concentration but the activity is reduced substantially at lower concentrations. Oxidized samples still exhibit some antibac- terial activity (50e60%) which is due to TBPs and active chlorine species present in the liquid phase. The latter are generated from chloride ions and enhance considerably AMX degradation rates. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction In recent years, electrochemical advanced oxidation technolo- gies have gained considerable attention for the destruction of persistent organic compounds (Antonin et al., 2015) and/or the inactivation of pathogens (Long et al., 2015) in wastewaters. In particular, the electrochemical mineralization of organic pollutants, i.e. their rapid conversion to carbon dioxide and water, is a rela- tively new approach in wastewater management suitable for in- dustrial effluents of moderate concentration, i.e. COD <5 g/L (Comninellis et al., 2008). This technology is based on the use of high oxidation power anodes and it consumes electrical energy for the mineralization of organic pollutants. An ideal anode for this type of treatment is the boron-doped diamond (BDD) electrode characterized by high reactivity to- wards organics oxidation and efficient use of electrical energy. BDD can generate weakly adsorbed hydroxyl radicals on the anode that are used to mineralize various organics, including the relatively refractory short-chain acids. Furthermore, BDD anodes exhibit high stability, low background current and wide potential window (Anglada et al., 2009; Antonin et al., 2015). The occurrence and fate of emerging micro-pollutants in the environment has attracted enormous attention in the past 15e20 * Corresponding author. E-mail address: mantzavinos@chemeng.upatras.gr (D. Mantzavinos). Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman http://dx.doi.org/10.1016/j.jenvman.2016.04.035 0301-4797/© 2016 Elsevier Ltd. All rights reserved. Journal of Environmental Management 195 (2017) 100e109